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● When used in a PVST+ network, STP loop guard is performed per-port or per-port channel at a VLAN level. If no BPDUs
are received on a VLAN interface, the port or port-channel transitions to a Loop-Inconsistent (Blocking) state only for this
VLAN.
To enable a loop guard on an STP-enabled port or port-channel interface, use the following command.
● Enable loop guard on a port or port-channel interface.
INTERFACE mode or INTERFACE PORT-CHANNEL mode
spanning-tree {0 | mstp | rstp | pvst} loopguard
○ 0: enables loop guard on an STP-enabled port assigned to instance 0.
○ mstp: enables loop guard on an MSTP-enabled port.
○
rstp: enables loop guard on an RSTP-enabled port.
○ pvst: enables loop guard on a PVST-enabled port.
To disable STP loop guard on a port or port-channel interface, use the no spanning-tree 0 loopguard command in an
INTERFACE configuration mode.
To verify the STP loop guard configuration on a port or port-channel interface, use the show spanning-tree 0 guard
[interface interface] command in a global configuration mode.
Displaying STP Guard Configuration
To display the STP guard configuration, use the following command.
The following example shows an STP network (instance 0) in which:
● Root guard is enabled on a port that is in a root-inconsistent state.
● Loop guard is enabled on a port that is in a listening state.
● BPDU guard is enabled on a port that is shut down (Error Disabled state) after receiving a BPDU.
● Verify the STP guard configured on port or port-channel interfaces.
show spanning-tree 0 guard [interface interface]
DellEMC#show spanning-tree 0 guard
Interface
Name Instance Sts Guard type
--------- -------- --------- ----------
Te 1/1/1 0 INCON(Root) Rootguard
Te 1/2/1 0 LIS Loopguard
Te 1/3/1 0 EDS (Shut) Bpduguard
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Spanning Tree Protocol (STP)